Relationships in microsoft access 2013 free download

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Resolved my issue. Easy to follow. Access More Not enough pictures. You can override these initial default values in your query, but the values supplied by the relationship will often prove to be the correct ones. When you drag a field from an «other» unrelated table and then complete the Lookup Wizard, a new one-to-many relationship is automatically created between the table in the Field List pane and the table to which you dragged the field.
 
 

 

Download Microsoft Access Runtime from Official Microsoft Download Center.Video: Create table relationships (Access basics, part 2)

 

Therefore, for each record in the Orders table, there can be many records in the Products table. In addition, for each record in the Products table, there can be many records in the Orders table. This relationship is called a many-to-many relationship. Note that to detect existing many-to-many relationships between your tables, it is important that you consider both sides of the relationship. To represent a many-to-many relationship, you must create a third table, often called a junction table, that breaks down the many-to-many relationship into two one-to-many relationships.

You insert the primary key from each of the two tables into the third table. As a result, the third table records each occurrence, or instance, of the relationship. For example, the Orders table and the Products table have a many-to-many relationship that is defined by creating two one-to-many relationships to the Order Details table. One order can have many products, and each product can appear on many orders. In a one-to-one relationship, each record in the first table can have only one matching record in the second table, and each record in the second table can have only one matching record in the first table.

This relationship is not common because, most often, the information related in this way is stored in the same table. You might use a one-to-one relationship to divide a table with many fields, to isolate part of a table for security reasons, or to store information that applies only to a subset of the main table.

When you do identify such a relationship, both tables must share a common field. You can create table relationships explicitly by using the Relationships window, or by dragging a field from the Field List pane. Access uses table relationships to decide how to join tables when you need to use them in a database object. There are several reasons why you should create table relationships before you create other database objects, such as forms, queries and reports. To work with records from more than one table, you often must create a query that joins the tables.

The query works by matching the values in the primary key field of the first table with a foreign key field in the second table. For example, to return rows that list all of the orders for each customer, you construct a query that joins the Customers table with the Orders table based on the Customer ID field. In the Relationships window, you can manually specify the fields to join. But, if you already have a relationship defined between the tables, Access supplies the default join, based on the existing table relationship.

In addition, if you use one of the query wizards, Access uses the information it gathers from the table relationships you have already defined to present you with informed choices and to prepopulate property settings with appropriate default values.

When you design a form or report, Access uses the information it gathers from the table relationships you have already defined to present you with informed choices and to prepopulate property settings with appropriate default values. Table relationships are the foundation upon which you can enforce referential integrity to help prevent orphan records in your database. An orphan record is a record with a reference to another record that does not exist — for example, an order record that references a customer record that does not exist.

When you design a database, you divide your information into tables, each of which has a primary key. You then add foreign keys to related tables that reference those primary keys. These foreign key-primary key pairings form the basis for table relationships and multi-table queries. Referential integrity, which is dependent on table relationships, helps ensure that references stay synchronized.

When you design a database, you divide your database information into many subject-based tables to minimize data redundancy. You then give Access a way to bring the data back together by placing common fields into related tables. For example, to represent a one-to-many relationship you take the primary key from the «one» table and add it as an additional field to the «many» table. To bring the data back together, Access takes the value in the «many» table and looks up the corresponding value in the «one» table.

In this way the values in the «many» table reference the corresponding values in the «one» table. Suppose you have a one-to-many relationship between Shippers and Orders and you want to delete a Shipper. If the shipper you want to delete has orders in the Orders table, those orders will become «orphans» when you delete the Shipper record. The orders will still contain a shipper ID, but the ID will no longer be valid, because the record that it references no longer exists.

The purpose of referential integrity is to prevent orphans and keep references in sync so that this hypothetical situation never occurs. You enforce referential integrity by enabling it for a table relationship.

Once enforced, Access rejects any operation that violates referential integrity for that table relationship. This means Access will reject both updates that change the target of a reference, and deletions that remove the target of a reference.

For such cases, what you really need is for Access to automatically update all the effected rows as part of a single operation. That way, Access ensures that the update is completed in full so that your database is not left in an inconsistent state, with some rows updated and some not. When you enforce referential integrity and choose the Cascade Update Related Fields option, and you then update a primary key, Access automatically updates all fields that reference the primary key.

It’s also possible you might have a valid need to delete a row and all related records — for example, a Shipper record and all related orders for that shipper. When you enforce referential integrity and choose the Cascade Delete Related Records option, and you then delete a record on the primary key side of the relationship, Access automatically deletes all records that reference the primary key.

To view your table relationships, click Relationships on the Database Tools tab. The Relationships window opens and displays any existing relationships.

If no table relationships have been defined and you are opening the Relationships window for the first time, Access prompts you to add a table or query to the window.

Click File , click Open , and then select and open the database. On the Database Tools tab, in the Relationships group, click Relationships. On the Design tab, in the Relationships group, click All Relationships. This displays all of the defined relationships in your database. Note that hidden tables tables for which the Hidden check box in the table’s Properties dialog box is selected and their relationships will not be shown unless the Show Hidden Objects check box is selected in the Navigation Options dialog box.

A table relationship is represented by a relationship line drawn between tables in the Relationships window. A relationship that does not enforce referential integrity appears as a thin line between the common fields supporting the relationship.

When you select the relationship by clicking its line, the line thickens to indicate it is selected. This is useful for hierarchical relationships such as parts lists, employee to supervisor reporting, customer referrals, etc.

These are all recursive relationships. The purpose of this article is show how to create a Microsoft Access query based on these recursive relationships. We will consider the one-to-many case, the most common, in this article. You can download the Microsoft Access sample database, SelfJoin. A downloadable PowerPoint presentation version of this article can be found on Slideshare. We want to construct a query that will list all employees and their supervisor, if they have one.

The employees and their supervisors are in a single employees table. After all, the supervisors are also employees. Database Design. Relationship Designer. It is the same as the Factory sample database design. Note the MgrNo foreign key. It actually references the EmpNo in the same table. Below is a screenshot of the sample data in the employees table. The MgrNo field references the EmpNo field in the same table.

Betty reports to Alicia who in turn reports to Mary. In this example Mary does not have a direct supervisor. This example is similar to many recursive relationships in which the top of the tree is denoted by a null foreign key. Ou r self join query will be a normal query, joining two tables. The difference is that this time the two tables are really the same table.

Just add the employees table twice to the query designer. The next step is to assign an alias to the second employees table above. Right click on the table name in the MS Access query designer and assign an alias as shown below. Call it managers. This step is not strictly necessary but your query will be more meaningful if you do it. What this does is give the second table what is called a table alias which is another name for the table.

All references to the table must then use this alias. Table aliases are often used in SQL to give a table a short name that a query can use. They are not so common in MS Access but are, nevertheless, helpful here.

Create the relationship between the two tables.